Moose Cree First Nation (MCFN) has long advocated for protection of the abundant peatlands within the Moose Cree homelands in boreal Ontario. They have specifically called for the establishment of a protected area in the North French River watershed because of its great cultural and ecological significance. Here, we present the results of collaborative analyses on a series of more than 20 peat cores collected across the watershed. The goals of the project included quantification of peat carbon stocks and accumulation rates, and analyses of changes in peat organic matter quality for assessment of stability in the context of climate warming and other disturbances. Peatland establishment in the watershed initiated in the headwaters approximately 8000 years before present, following retreat of proglacial Lake Ojibway. Deep peats developed at suitable sites since then, with peat depths approaching 5 m at several locations. Total carbon stocks in the upper part of the watershed vary considerably, with high values in excess of 160 kg C m-2 at sites where Sphagnum peatlands established early, and 75-80 kg C m-2 in peatlands with similar depths but different histories. In the lower part of the watershed within the James Bay Lowlands, peat establishment took after 5000 years before present, following the marine incursion of the Tyrrell Sea and resulted in the formation of continuous and extensive peatlands. Taken as a whole, our analyses confirm the importance of this watershed in terms of its high peat carbon stocks, and the considerable diversity of peat types.